Method of making high-bulk yarns



United States Patent Office 3,012,397 Patented Dec. 12, 1961 3,012,397METHOD OF MAKING HIGH-BULK YARNS Henri Servage, Cremieu, Isere, France,assignor to Mouiinage ct Retorderie de Chavanoz, Chavanoz (Isere),France, a company incorporated of France No Drawing. Filed Nov. 30,1959, Ser. No. 856,014 14 Claims. (Cl. 57-157) This invention relates tohigh bulk yarns, and more particularly to an improved process for theproduction of high-curl polyacrylonitrile and polyester yarns of thehigh-bulk type, and to yarns produced by such process.

The high-curl yarns called high-bulk yarns in the textile industry havebeen obtained notably from polyamides by high twisting, setting of thetwist and untwisting, either in a number of successive operations, or bythe applying of a false twist which is heat-set while it is beingapplied. I

When either of the aforementioned methods is attempted to be practicedwith yarns of acrylonitrile polymers or copolymers, or of polyesters,the results obtained are not entirely satisfactory. That is to say, theincrease in volume of yarns, generally termed the high-bulk effect, isof relatively low order and normally insufficient for many commercialpurposes.

It is recognized by those skilled in the art that yarns composed ofthese particular fibers may not be expected to produce the resultsachieved with polyamides and various other thermoplastic yarns merely bythe practice of methods applicable to polyamides and such other yarns.

According to the present invention it has, however, been found that asubstantially increased high-bulk effect may be obtained with yarns ofacrylonitrile polymers and co-polymers and of polyesters, by a furtherthermal treatment of the yarn subsequent to the twisting, twistsetting,and untwisting operations of the prior art. This further thermaltreatment is preferably effected while the yarn is under no appreciabletension, and may be effected while the yarn is either in skein form, inwhich case the thermal treatment is preferably effected by placing theskeins in an oven at a moderate elevated temperature, or such may beeffected continuously as by linearly passing the yarn continuouslythrough a heating zone at a moderate temperature, and preferably underno appreciable tension as by overfeed of the yarn through this heatingzone. The continuous thermal post treatment may be carried out forexample by passing the yarn axially through a tube having an effectivetemperature of approximately 150 C., or by bringing the yarn intocontact, without appreciable tension, also as by permissive or positiveoverfeed, with a convex surface having a temperature of the order ofapproximately 95 C.

While the invention may be practiced by applying the basic method stepsto a single yarn, it is more advantageous and pref rable to combine, asby doubling, two treated yarns which have undergone opposite falsetwists (i.e. one yarn having undergone a false Z-twist and a secondsimilar length of yarn having undergone a false S-twist). Subsequent tothis combining of the two oppositely false twisted yarns, the combinedyarn is subjected to the post thermal treatment as discussed above,preferably without appreciable tension, to thereby efiect a high-bulk inthe combined yarn.

Further, according to another aspect of the invention it is preferableto permit a slight filament heat shrinkage of the yarn, for example ofthe order of 0.5-2%, during the original high twisting of the base yarn,and to effect a further mechanical or spatial shrinkage of the order of512% as the individual treated yarn proceeds to its takeup bobbin, inaccordance with the principle of French Certificate of Addition 67,751of March 31, 1955, to French Patent 1,054,338. The additional subsequentheat treatment of the yarn in order to effect the highbulking thereof isthen preferably carried out either on the individual yarn if such is tobe used as a final product as such, or preferably on a doubled yarn ofoppositely twist-treated yarns. By varying the shrinkage permittedduring the false twisting and during the winding of the individual yarnonto the takeup bobbin preceding the subsequent post thermal treatmentas discussed above, highbulk yarns can be obtained which have varyingelasticity and varying stretch.

The invention will be more readily understood from a practical exampleof the practice thereof, which example will naturally be understood tobe illustrative only.

Example A -denier yarn having an original twist of S-turns or Z-turnsper meter and consisting of an acrylonitrile co-polymer containing 5% ofrnethylmethacrylate, is given a twist of 2,100 turns per meter on adevice such as described in French Patent 1,054,338 of January 23, 1952,French Certificates of Addition 63,963 of June 19, 1953, and 66,140 ofSeptember 22, 1954, and notably French Patent 1,140,992 of January 6,1956. The false-twist tubes for imparting the false twist according tothese patents are employed in the instant example at a speed of 50,000rpm, and the false twist is imparted in the opposite direction to theinitial twist of the yarn. As in accordance with the above mentionedFrench patents and certificates of addition, the yarn is heated beforeit enters the rotating false-twist tubes as by tubular resistors whichare disposed directly preceding the rotating tubes and are maintained ata temperature of, for example, 220-225 C. in the case of a yarn whichhas not yet undergone any heat setting. This heating of the yarnpreceding its a passage through the rotating false twist tubes serves toset the false twist in the yarn. When the yarn has already undergoneheat setting prior to this heating and false twist action the tubularresistors are maintained at a temperature between the temperature of thefirst heat heat setting thereof and a temperature 5 C. below thesoftening point of the material of the yarn.

A slight filament contracting heat shrinkage of the order of 0.52% ispreferably permitted during the false twisting of the yarn, as byoverfeeding the yarn into the twist zone by this amount. Also, a furthermechanical or spatial effective overall yarn shrinkage of 542% iseffected as a result of the torque imparted to the yarn by the falsetwisting and setting operation, between the takeup bobbin and the feedroll delivering the yarn thereto, in accordance with the principle ofCertificate of Addition 67,751 of March 31, 1955, to French Patent1,054,338.

A length of treated yarn having undergone a false Z- twist and a similarlength having undergone a false 8- twist are assembled as by doubling atturns per meter. The assembled yarn is thereafter subjected in skeinform to an oven treatment at 90-95 C. and without appreciable tensionthereon.

This subsequent oven treatment of the yarn in skein form imparts animproved high-bulk effect to the yarn, which yarn also has elastic andstretch characteristics, the degree of high-bulk, elasticity and stretchbeing dependent upon the shrinkage permitted during the false twistingand during the Winding as mentioned above.

Although this particular illustrative example is described with thesubsequent thermal treatment of the yarn being effected while the yarnis in skein form, or in other words discontinuous post heat treatmentunder no appreciable tension, in many instances of commercial productiona continuous treatment process is much more advantageous. As a preparedalternative to the skein post-heat-treatment, or discontinuoous process,a continuous post-heat-treatment may be carried out, as for example bypassing the yarn axially and without appreciable tension through aheater tube maintained at for example 150 C., or the bringing of theyarn into contact, without appreciable tension, with a convex heater.bulk type, comprising twisting in a first direction a first yarn ofmaterial selected from the group consisting of polyacrylonitriles,acrylonitrile co-polymers, and polyesters, setting of said firstdirectional twist and untwisting of said yarn, twisting in the oppositedirection to said first direction, a second yarn selected from saidgroup, setting of said twist in said second yarn and untwisting of saidsecond yarn, permitting filament heat shrinkage of each of said yarnsduring said firstmentioned twisting thereof, overfeeding andmechanically spatially shrinking ,said yarns between approximately to12% subsequent to said first mentioned filament heat shrinkage,combining said yarns to form a combined yarn, and then subjecting saidcombined yarn to a subsequent heat treatment while under substantiallyno appreciable tension.

' 2. The method according to claim 1 wherein said filament heatshrinkage is in the range of approximately 0.5-2%.

3. The method according to claim 1 wherein said combined yarn issubjected to said heat treatment while continuously linearly moving saidyarn through a heating zone.

4. The method according to claim 3 wherein said yarn is subjected tosaid subsequent heat treatmentby continuous linear passage through aheater tube having an efiective temperature of approximately 150 C.

5. The method according to claim 3 wherein said subsequent heattreatment is efiected by continuous linear movement of said yarn overand in contact with a contact heater having an 'efiective temperature ofapproximately 95 C. a

6. The method according to claim 1 wherein said combined yarn issubjected in skein form to an oven heat treatment at approximately 90-95C.

7. The method according to claim 1 wherein said yarns are combined bydoubling and twisting.

8. The method according to claim 7 wherein said doubling and twisting isof the order of turns per meter.

9. The method of producing high-curl polyacrylonitrile, acrylonitrileco-polymer, and polyester yarns of the high-bulk type, comprisingtwisting in a first direction a yarn of material selected from the groupconsisting of polyacrylonitriles, acrylonitrile co-polymers, andpolyesters, setting of said first directional twist and untwisting ofsaid yarn, permitting filament heat shrinkage of said yarn during saidfirst mentioned twisting thereof, overfeeding and mechanically spatiallyshrinking said yarn between approximately 5-12% subsequent to said firstmentioned filament heat shrinkage, and then subjecting said yarn to asubsequent heat treatment while under substantially no appreciabletension. 7

10. The method according to claim 9 wherein said filament heat shrinkageis in the range of approximately O.5-2%.

11. The method according to claim 9 wherein said yarn is subjected tosaid subsequent heat treatment while continuously linearly moving saidyarn through a heating zone.

12. The method according to claim 11 wherein said yarn is subjected tosaid subsequent heat treatment by continuous linear passage through aheater tube having an effective temperature of approximately. C.

13. The method according to claim 11 wherein said subsequent heattreatment is effected by continuous linear movement of said yarn overand in contact witha contact heater having an effective temperature ofapproximately 95 C.

14. The method according to claim 9 wherein said yarn is subjected inskein form to an oven heat treatment at approximately 90-95 C.

' References Cited in the file of this patent UNITED STATES PATENTS

1. THE METHOD OF PRODUCING HIGH-CURL POLYACRYLONITRILE, ACRYLONITRILECO-POLYMER, AND POLYESTER YARNS OF THE "HIGHBULK" TYPE, COMPRISINGTWISTING IN A FIRST DIRECTION A FIRST YARN OF MATERIAL SELECTED FROM THEGROUP CONSISTING OF POLYACRYLONITRILES, ACRYLONITRILE CO-POLYMERS, ANDPOLYESTERS, SETTING OF SAID FIRST DIRECTIONAL TWIST AND UNTWISTING OFSAID YARN, TWISTING IN THE OPPOSITE DIRECTION TO SAID FIRST DIRECTION, ASECOND YARN SELECTED FROM SAID GROUP, SETTING OF SAID TWIST IN SAIDSECOND YARN AND UNTWISTING OF SAID SECOND YARN, PERMITTING FILAMENT HEATSHRINKING OF EACH OF SAID YARNS DURING SAID FIRST MENTIONED TWISTINGTHEREOF, OVERFEEDING AND MECHANICALLY SPATIALLY SHRINKING SAID YARNSBETWEEN APPROXIMATELY 5 TO 12% SUBSEQUENT TO SAID FIRST MENTIONEDFILAMENT HEAT SHRINKAGE, COMBINING SAID YARNS TO FORM A COMBINED YARN,AND THEN SUBJECTING SAID COMBINED YARN TO A SUBSEQUENT HEAT TREATMENTWHILE UNDER SUBSTANTIALLY NO APPRECIABLE TENSION.